1. Field of the Invention
The invention relates to an electric switch in which the arc generated between two mutually mobile contacts inside a chamber is sheared between two insulating walls, one of which belongs to an insulating screen that is quickly inserted between the two contacts, resulting in total insulation between them.
2. Description of the Prior Art
This type of switch, which can be used to advantage in automatic or manual opening protection devices, is described for instance in the French patent application No. 83 01749, filed on Feb. 4, 1983 by the Applicant. These switches can also be used in circuit opening apparatus with high rated current.
In some of these known switches where the screen movement is caused by the release of energy accumulated in a spring at the moment the contacts part, screen motion speed varying as an increasing function of current level may be wanted, to avoid quick current rise. Besides, a movement energy that needs no mechanical setting or resetting after automatic opening is often desirable.
In other screened switches, where screen motion is driven by an electro-magnetic striker supplied by the current flowing in the switch, the speed imparted to the screen, although to an extent it is in increasing function of the current flowing in the magnetic coil, cannot exceed a certain threshold owing to the magnetic saturation that develops.
In these two types of known devices, screen velocity could be increased by increasing the potential energy of a previously set driving spring, to be released either by the movement of the contacts or by a magnetic coil tripping device; however, this would require a more costly and more delicate resetting system, owing to the amplitude of the forces involved and the wear of the mechanical parts controlling them.
In any case, as high a pressure as possible should be maintained for some time in a switch arc chamber, in order to take advantage of the favourable effect of pressure on arc voltage.